Clamping device in main shaft driving device for machine tool

ABSTRACT

A clamping device in a main shaft driving device for a machine tool, which rotationally drives a main shaft, wherein the main shaft is rotatably supported by a frame. The clamping device includes a clamp piston, a pressure chamber and an operating fluid supplying mechanism, wherein the clamp piston has a first pressure-receiving surface and a second pressure-receiving surface, the first pressure-receiving surface receiving the spring force of a spring member, the second pressure-receiving surface receiving pressure of an operating fluid, wherein the operating fluid supplying mechanism includes a switching portion that selectively supplies the corresponding operating fluid from a common operating fluid supply source to at least one of a first pressure chamber and a second pressure chamber, the first pressure chamber being formed by the first pressure-receiving surface and the frame, the second pressure chamber being formed by the second pressure-receiving surface and the frame.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 12/613,042,filed Nov. 5, 2009, which claims priority of Japanese Patent ApplicationNo. 2008-296141, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a clamping device in a main shaftdriving device for a machine tool. More particularly, the presentinvention relates to a clamping device in a machine-tool main shaftdriving device that rotationally drives by a driving device a main shaftrotatably supported by a frame and having a member that is rotationallydriven secured to one end thereof. This clamping device includes abraking member, a pressure chamber, and an operating fluid supplyingmechanism. The braking member is provided at a side of the frame, andhas a pressure-receiving surface and a braking portion. Thepressure-receiving surface receives pressure of an operating fluid. Thebraking portion causes a press-contact force to act upon the main shaft.The pressure chamber is formed by the pressure-receiving surface and theframe. The operating fluid supplying mechanism is provided for supplyingthe operating fluid from an operating fluid supply source to thepressure chamber. In this clamping device, the press-contact force iscaused to act upon the main shaft by displacing the braking portiontowards the main shaft by the pressure of the operating fluid that issupplied to the pressure chamber.

2. Description of the Related Art

As a main shaft driving device used in a machine tool, there is arotation indexing table device that rotationally drives a circulartable, on which, for example, a workpiece is placed, through a mainshaft. The rotation indexing table device is used for indexing anangular position of the main shaft (circular table) by rotationallydriving the main shaft, and processing a workpiece at the indexedangular position. Therefore, the rotation indexing table device includesa clamping device for maintaining the indexed angular position.

A related art of such a rotation indexing table device including aclamping device described above is discussed in Japanese UnexaminedPatent Application Publication No. 2006-95668 (Patent Document 1). Asdriving means of a circular table, the rotation indexing table device inPatent Document 1 uses a direct-drive motor (hereunder referred to as“DD motor”) that rotationally drives the main shaft without using drivetransmitting means such as a gear. In addition, the rotation indexingtable device in Patent Document 1 includes as a clamping device a discclamping device in which a brake plate (clamp disc) is mounted to thecircular plate (secured to the main shaft that is rotationally driven bythe DD motor) so as to be incapable of relative rotation; and in which apiston is urged towards the brake plate by operating fluid and the brakeplate is held by cooperation of a frame and the piston.

More specifically, the clamping device in the rotation indexing tabledevice in Patent Document 1 switches between a clamped state and anunclamped state of the circular table by introducing operating fluid.The piston is normally urged towards the brake plate by a compressionspring, and stops rotation of the table by friction as a result ofcontacting the brake plate while introduction of operating fluid isstopped. When the table is rotated, the operating fluid is introduced,and the piston is moved against urging force of the compression springto set the circular table in the unclamped state.

Accordingly, in the related main shaft driving device, the clampingdevice is generally set in the unclamp state when the main shaft isrotated. Even when a finishing operation is performed while continuouslyrotating the workpiece, the operation is performed while the clampingdevice is in the unclamp state.

When the finishing operation is performed while continuously rotatingthe workpiece, the main shaft driving device receives a load from acutter that processes the workpiece. This load constantly varies evenunder a constant processing condition. Therefore, rotation state of themain shaft driving device is affected by the variations in the load thatis received from the cutter.

When the DD motor is used as the driving means of the main shaft as inthe rotation indexing table device discussed in Patent Document 1,control of the DD motor is carried out while correcting deviation ofrotational angle (amount of rotation) of the main shaft driving deviceoccurring due to the main shaft driving device being influenced by theload that it receives from the cutter as mentioned above, on the basisof feedback of the rotational angle (the amount of rotation) from arotation detector of the main shaft driving device. However, due to thevariations in the load received from the cutter, the rotation of the DDmotor resulting from the control may not be able to follow thedeviation. Therefore, the rotation of the DD motor is not necessarilyuniform, and may include pulsation. In addition, when a speed reducerincluding gears is used as the driving means of the main shaft, therotation state of the main shaft may include pulsation in a backlashrange of the gears due to the influence of the variations in load thatis received from the cutter.

As a result, pulsation occurs in the rotation state of the main shaftdriving device, thereby deteriorating surface roughness of a finishedsurface of the workpiece.

When the clamping device is in the unclamp state, the rigidity of themain shaft of the main shaft driving device primarily depends upon therigidities of the bearings. The rigidities of the bearings dependlargely upon compression of the bearings. Therefore, when the rigidityof the main shaft is required, the compression of the bearings is madelarge. However, in order to withstand the large compression, thebearings themselves need to be large. When the bearings are made large,deflection precision is reduced. Therefore, indexing precision isreduced, as a result of which processing precision is reduced. Inaddition, since the larger the diameters of the bearings, the higher thecost, manufacturing cost of the device is increased.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide astructure in the aforementioned main shaft driving device, in whichpulsation in a rotation state of the main shaft driving device isreduced when a finishing operation is performed while continuouslyrotating a workpiece, and in which rigidity of the main shaft isincreased even if a bearing is not made large.

A first aspect of the present invention presupposes a clamping device ina main shaft driving device for a machine tool. The main shaft drivingdevice rotationally drives a main shaft by a driving device. The mainshaft is rotatably supported by a frame and has a member that isrotationally driven secured to an end portion thereof. The clampingdevice includes a braking member, a pressure chamber, and an operatingfluid supplying mechanism, the braking member provided at a side of theframe and including a pressure-receiving surface and a braking portion,the pressure-receiving surface receiving pressure of an operating fluid,the braking portion causing a press-contact force to act upon the mainshaft, the pressure chamber being formed by the pressure-receivingsurface and the frame, the operating fluid supplying mechanism beingprovided for supplying the operating fluid from an operating fluidsupply source to the pressure chamber, wherein the press-contact forceis caused to act upon the main shaft by displacing the braking portiontowards the main shaft by the pressure of the operating fluid that issupplied to the pressure chamber.

On the basis of the aforementioned object, according to the first aspectdirected to the clamping device, the clamping device is such that thebraking member has a first pressure-receiving surface and a secondpressure-receiving surface, which extend orthogonally to a direction inwhich the braking portion causes press-contact forces to act upon themain shaft; the operating fluid supplying mechanism includes a switchingportion that selectively supplies the operating fluid from a commonoperating fluid supply source to at least one of first and secondpressure chambers, the first pressure chamber being formed by the firstpressure-receiving surface and the frame, the second pressure chamberbeing formed by the second pressure-receiving surface and the frame; andthe braking member is formed so that the braking portion causes thepress-contact forces that differ from each other to act upon the mainshaft when pressures of the operating fluid that are equal to each otheract upon the first pressure-receiving surface and secondpressure-receiving surface, respectively.

In the clamping device according to the first aspect, the braking membermay be such that the braking portion causes the press-contact force toact upon the main shaft when the pressure of the operating fluid actsupon the second pressure-receiving surface, the press-contact forcecausing the main shaft to be set in a partially clamped state; and, whenthe main shaft is to be set in a completely clamped state, the operatingfluid supplying mechanism may be such as to supply the operating fluidto at least the first pressure chamber by the switching portion.Further, the braking member may be formed so that the area of the firstpressure-receiving surface and the area of the second-pressure receivingsurface differ from each other.

A second aspect of the present invention presupposes another clampingdevice in a main shaft driving device for a machine tool. The main shaftdriving device rotationally drives a main shaft by a driving device. Themain shaft is rotatably supported by a frame and has a member that isrotationally driven secured to an end portion thereof. The clampingdevice includes a clamp piston, a pressure chamber, and an operatingfluid supplying mechanism, the clamp piston being provided so as to bedisplaceable in an axial direction of the main shaft with respect to theframe, the clamp piston including a pressure-receiving surface and abraking portion, the pressure-receiving surface receiving pressure of anoperating fluid, the braking portion causing a press-contact force toact upon the main shaft, the pressure chamber being formed by thepressure-receiving surface and the frame, the operating fluid supplyingmechanism being provided for supplying the operating fluid from anoperating fluid supply source to the pressure chamber, wherein thepress-contact force is caused to act upon the main shaft by displacingthe clamp piston towards the main shaft by the pressure of the operatingfluid that is supplied to the pressure chamber.

According to the second aspect directed to the clamping device, theclamping device includes a spring member that urges the clamp piston ina first direction, which is the same as a direction in which the brakingportion causes the press-contact force to act upon the main shaft, thespring member causing a spring force to act upon the pressure-receivingsurface, the spring force causing the press-contact force that causesthe main shaft to be set in a partially clamped state to act upon themain shaft by the braking portion; the clamp piston has a firstpressure-receiving surface and a second pressure-receiving surface, thefirst pressure-receiving surface extending in a second direction that isorthogonal to the first direction and receiving pressure of an operatingfluid in the first direction, the first pressure-receiving surfacereceiving the spring force of the spring member, the secondpressure-receiving surface extending in the second direction andreceiving pressure of an operating fluid in a direction opposite to thefirst direction; and the operating fluid supplying mechanism includes aswitching portion that selectively supplies the corresponding operatingfluid from a common operating fluid supply source to at least one of thefirst and second pressure chambers, the first pressure chamber beingformed by the first pressure-receiving surface and the frame, the secondpressure chamber being formed by the second pressure-receiving surfaceand the frame.

According to the first aspect of the present invention, the brakingmember has a first pressure-receiving surface and a secondpressure-receiving surface, which extend orthogonally to a direction inwhich the braking portion causes press-contact forces to act upon themain shaft; the operating fluid supplying mechanism includes a switchingportion that selectively supplies the operating fluid from a commonoperating fluid supply source to at least one of first and secondpressure chambers, the first pressure chamber being formed by the firstpressure-receiving surface and the frame, the second pressure chamberbeing formed by the second pressure-receiving surface and the frame; andthe braking member is formed so that the braking portion causes thepress-contact forces that differ from each other to act upon the mainshaft when pressures of the operating fluid that are equal to each otheract upon the first pressure-receiving surface and secondpressure-receiving surface, respectively. By virtue of this structure,it is possible for the braking portion of the clamping device to causedifferent press-contact forces to act upon the main shaft by selectivelysupplying operating fluids of the same pressure from the commonoperating fluid supply source without adjusting the pressure of theoperating fluid.

Therefore, if the braking portion causes a press-contact force thatcauses the main shaft to be in the clamped state to act upon the mainshaft when the pressure of the operating fluid acts upon one of thepressure-receiving surfaces (such as the second pressure-receivingsurface), the main shaft can be easily set in the partially clampedstate by only selectively switching the supply of the operating fluid.Here, the term “partially clamped state” refers to a state in which theclamping device causes a press-contact force that applies rotationalresistance allowing rotation of the main shaft to act upon the mainshaft.

According to the second aspect of the present invention, the clampingdevice includes a spring member that urges the clamp piston in a firstdirection, which is the same as a direction in which the braking portioncauses the press-contact force to act upon the main shaft, the springmember causing a spring force to act upon the pressure-receivingsurface, the spring force causing the press-contact force that causesthe main shaft to be set in a partially clamped state to act upon themain shaft by the braking portion; the clamp piston has a firstpressure-receiving surface and a second pressure-receiving surface, thefirst pressure-receiving surface extending in a second direction that isorthogonal to the first direction and receiving pressure of an operatingfluid in the first direction, the first pressure-receiving surfacereceiving the spring force of the spring member, the secondpressure-receiving surface extending in the second direction andreceiving pressure of an operating fluid in a direction opposite to thefirst direction; and the operating fluid supplying mechanism includes aswitching portion that selectively supplies the corresponding operatingfluid from a common operating fluid supply source to at least one of thefirst and second pressure chambers, the first pressure chamber beingformed by the first pressure-receiving surface and the frame, the secondpressure chamber being formed by the second pressure-receiving surfaceand the frame. By virtue of this structure, a press-contact force thatsets the main shaft in the normally partially clamped state acts uponthe main shaft. By causing the pressure of the operating fluid to actupon the second pressure-receiving surface, it is possible to cause themain shaft to be set in the unclamped state, in which the clamp pistonis displaced towards the second direction against the spring force ofthe spring member so that a press-contact force does not act upon themain shaft. In addition, by causing the pressure of the operating fluidto act upon the first pressure-receiving surface, the clamp piston isurged towards the first direction by the pressure of the operating fluidas well as by the spring force of the spring member, so that the mainshaft can be in the completely clamped state. In this way, according tothe second invention, the partially clamped state, the completelyclamped state, and the unclamped state can be easily realized by onlyselectively switching the supply of operating fluid without adjustingthe pressure of the operating fluid.

In addition, if a finishing operation is performed on a workpiece whilecontinuously rotating the workpiece by the main shaft driving devicewhen the main shaft is in the partially clamped state, variations inload that the main shaft driving device receives from the cutter thatprocesses the workpiece can be restricted by rotational resistance. Thismakes it possible to reduce pulsation in the control of the DD motor andpulsation within a gear backlash range, so that the rotational state ofthe main shaft driving device can be made stabilized to a uniform state.

Further, since the clamping device provides rigidity to the main shaftin the main shaft driving device, it is possible to increase therigidity of the main shaft without increasing the size of the bearing.As a result, it is possible to provide good surface roughness of afinished surface of the workpiece. In addition, it is possible to use aworkpiece that is larger than a related workpiece using a bearing of thesame diameter. Accordingly, since a bearing having a small diameter canbe used, a high processing precision can be realized, and manufacturingcosts of the main shaft driving device for a machine tool can bereduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a first embodiment of a rotational resistancedevice of a main shaft driving device for a machine tool;

FIG. 2 is an enlarged explanatory diagram of the first embodiment of therotational resistance device of the main shaft driving device for themachine tool;

FIG. 3 is a side view of a second embodiment of a rotational resistancedevice of a main shaft driving device for a machine tool;

FIG. 4 is an enlarged explanatory diagram of the second embodiment ofthe rotational resistance device of the main shaft driving device forthe machine tool;

FIG. 5 is an enlarged explanatory diagram of the second embodiment ofthe rotational resistance device of the main shaft driving device forthe machine tool;

FIG. 6 is a side view of a third embodiment of a rotational resistancedevice of a main shaft driving device for a machine tool;

FIG. 7 is an enlarged explanatory diagram of the third embodiment of therotational resistance device of the main shaft driving device for themachine tool;

FIG. 8 is an enlarged explanatory diagram of the third embodiment of therotational resistance device of the main shaft driving device for themachine tool; and

FIG. 9 is an enlarged explanatory diagram of the third embodiment of therotational resistance device of the main shaft driving device for themachine tool.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 each show a rotation indexing table device 1 serving as amain shaft driving device for a machine tool according to the presentinvention. FIG. 1 is a general view thereof. In the description below,“axial direction” refers to an axial direction of a main shaft 4 a thatsupports a circular table 5 serving as a member that is rotationallydriven, and “radial direction” refers to a radial direction of thecircular table 5 and the main shaft 4 a, which are concentricallydisposed.

In FIG. 1, the rotation indexing table device 1 includes a main shaft 4a, which is rotatably supported by a frame 2 and which has the memberthat is rotationally driven secured to one end thereof; a driving device6 for rotationally driving the main shaft 4 a; and a clamping device 10,which maintains an indexed rotational angle of the main shaft 4 a. Theframe 2 is such that a portion serving as a surface for setting to themachine tool is a flat surface. The frame 2 is provided with acylindrical base portion 11 that surrounds the main shaft 4 a.

The frame 2 is formed by separately forming casing members 28 a and 28 band a base member 29 having the cylindrical base portion 11 formedthereat and by assembling these with a plurality of mounting bolts 27.However, the cylindrical base portion 11 may be formed as a separatemember, and may be mounted with, for example, a bolt.

The main shaft 4 a is inserted into the cylindrical base portion 11 inthe frame 2, and is rotatably supported to the frame 2 by bearings 3. Aflange 4 b and the circular table 5, serving as the member that isrotationally driven, are mounted to one end of the main shaft 4 a. Theother end of the main shaft 4 a is inserted into a hole 16 a of adisc-shaped projecting portion 16, mounted to the inner peripheral sideof the base member 29 with a plurality of mounting bolts 37, andprojects out from the hole 16 a.

The circular table 5 is fitted to a circular-table-side end surface(upper surface in FIG. 1) of the flange 4 b at a center hole 13 a. Withthe circular table 5 being positioned with respect to the flange 4 b bythe fitting operation, the circular table 5 is mounted to theaforementioned end surface of the flange 4 b by a plurality of mountingbolts 12. The flange 4 b is fitted to one end of the main shaft 4 a at acenter hole 13 b. With the flange 4 b being positioned with respect tothe main shaft 4 a by the fitting operation, the flange 4 b is mountedto an end surface of the main shaft 4 a by a plurality of mounting bolts51. A cylindrical holding portion 23 extending in the axial direction ofthe main shaft 4 a from an end surface opposite to the aforementionedend surface is integrally formed with the flange 4 b. The holdingportion 23 surrounds the base portion 11. The holding portion 23 and theflange 4 b are formed separately from the circular table 5, and aresecured to the circular table 5. However, the holding portion 23 and theflange 4 b may be integrally formed with the circular table 5. Theholding portion 23 may be integrally formed with the main shaft 4 a.

The main shaft 4 a is supported by the bearings 3 provided between theouter peripheral surface of the main shaft 4 a and the inner peripheralsurface of the base portion 11. In the illustrated embodiment, threebearings 3 are combined with each other and provided for supporting themain shaft 4 a. With an inner ring side of the bearings 3 beinginterposed between a stepped portion of the outer peripheral surface ofthe main shaft 4 a and a portion surrounding the center hole 13 b of theflange 4 b, the bearings 3 are secured to the main shaft 4 a. With anouter ring side of the bearings 3 being interposed between a steppedportion of the inner peripheral surface of the base portion 11 and anannular bearing holder 14, mounted to an end surface of the base portion11 by a mounting bolt 15, the bearings 3 are secured to the base portion11.

A sliding disc 43 that receives a press-contact force by the clampingdevice (described later) is mounted to the main shaft 4 a. The slidingdisc 43 is a resiliently deformable member formed of a disc-shaped thinplate, and is secured to the main shaft 4 a by a mounting bolt 19 at theinner peripheral portion of the sliding disc 43. The sliding disc 43 isdisposed such that a circular-table-5-side of the outer peripheralportion of the sliding disc 43 faces a surface 63 at a side opposite tothe circular table 5 in the axial direction of the stepped portion ofthe base portion 11. A surface at a side opposite to the circular table5 of the sliding disc 43 faces a circular-table-5-side surface of theprojecting portion 16 mounted to the base member 29. The surface 63 atthe side opposite to the circular table 5 at the stepped portion of thebase portion 11 corresponds to what is called a clamp surface, which isa surface where the sliding disc 43 is pressed and contacted when thesliding disc 43 receives a press-contact force from the clamping deviceas mentioned above.

Further, a detection ring 21 that constitutes a portion of a rotationdetector 20 is mounted to the other end of the main shaft 4 a thatprojects out from the hole 16 a of the projecting portion 16. Therotation detector 20 detects the rotational angle (amount of rotation)of the main shaft 4 a. The rotation detector 20 includes theaforementioned detection ring 21, mounted to the main shaft 4 a, and adetection sensor 22, mounted to the projecting portion 16 at a side ofthe frame 2. A space at the outer periphery of the main shaft 4 a at theother end side of the main shaft 4 a where the rotation detector 20 isprovided is covered with a cover member 18 mounted to the base member 29by a mounting bolt 17.

In the illustrated embodiment, as the driving device 6, a DD motor 9that rotationally drives the main shaft without driving transmittingmeans, such as a gear, is used. That is, in the embodiment, the DD motor9 corresponds to the driving device according to the present invention.The DD motor 9 is disposed concentrically with the main shaft 4 a in theaxial direction of the main shaft 4 a. The DD motor 9 includes a motorrotor 7, provided at the main shaft 4 a so as to be incapable ofrotating relatively thereto, and a motor stator 8, disposed so as tosurround the motor rotor 7 and provided at the frame 2 so as to beincapable of rotating relatively thereto. That is, the illustrated DDmotor 9 is what is called an inner rotor type. The DD motor 9 isconnected to a controlling device (not shown) of the machine tool, anddriving thereof is controlled by the controlling device.

With the motor rotor 7 being fitted to the outer peripheral surface ofthe holding portion 23 at the flange 4 b, the motor rotor 7 is mountedto the flange 4 b with a mounting bolt 24, inserted from the side of theflange 4 b, so as to be incapable of rotating relatively thereto.Therefore, the motor rotor 7 is incapable of rotating relatively to themain shaft 4 a to which the circular table 5 is secured.

With the inner peripheral surface of the motor stator 8 facing the outerperipheral surface of the motor rotor 7 and with a slight gap beingformed between it and the outer peripheral surface of the motor rotor 7,the motor stator 8 is mounted to the frame 2. More specifically, astator sleeve 25 is fitted to the inner peripheral surface of the casingmember 28 a in the frame 2, and the motor stator 8 is fitted to theinner peripheral surface of the stator sleeve 25 so as to be incapableof rotating relatively thereto. The stator sleeve 25 is mounted to theframe 2 by a mounting bolt 26 inserted from the base-member-29 side ofthe frame 2. Therefore, the motor stator 8 is incapable of rotatingrelatively to the frame 2 in the frame 2.

The clamping device 10 includes an annular clamp piston (serving as abraking member), a first pressure chamber 49 a, a second pressurechamber 49 b, and an operating fluid supplying mechanism 42. That is, inthe embodiment, the clamping device 10 is a disc-type clamping device inwhich the braking member is a clamp piston, the clamp piston causes apress-contact force to act upon the sliding disc 43, and rotationalresistance is applied to the sliding disc 43 by the clamp piston and theclamp surface 63.

In the illustrated embodiment, the clamp piston serving as a brakingmember includes a first piston member 44 a and a second piston member 44b. The first piston member 44 a is accommodated in an annular firstgroove 30 a of the projecting portion 16 so as to be movable in theaxial direction. The first groove 30 a is formed so as to open at asliding-disc-43 side in a portion facing the sliding disc 43 of theprojecting portion 16. Therefore, the first piston member 44 aaccommodated in the first groove 30 a is such that acircular-table-5-side end surface (=sliding-disc-43-side end surface)faces the sliding disc 43.

The first piston member 44 a has an annular projection provided at aportion thereof at the outer peripheral side of the sliding-disc-43-sideend surface so as to face the clamp surface 63. The projecting portioncontacts the sliding disc 43 and causes a press-contact force to actthereupon when the first piston member 44 a is displaced towards thesliding disc 43, and corresponds to a braking portion 44 c according tothe present invention. In addition, in the embodiment, the brakingportion 44 c causes a press-contact force to act upon the sliding disc43 towards the circular table 5 in the axial direction. This directioncorresponds to what is called in the invention “direction in which apress-contact force acts upon the main shaft 4 a,” and is hereunderreferred to as “clamp direction.” An end surface at a side opposite tothe sliding disc 43 of the first piston member 44 a corresponds to afirst pressure-receiving surface 35 a extending orthogonally to theclamp direction. In addition, a space surrounded by the firstpressure-receiving surface 35 a and the first groove 30 a corresponds tothe first pressure chamber 49 a to which operating fluid for displacingthe first piston member 44 a (braking portion 44 c) is supplied.

A return disc 52 is provided at a location between thepressure-receiving surface 35 a and a sliding-disc-43-side surface ofthe projecting portion 16. The return disc 52 is an elasticallydeformable member formed of a substantially donut-shaped thin plateprovided with a plurality of mounting holes (not shown) in a plane.Using mounting bolts 53, the mounting holes adjacent to each other arealternately mounted to the first piston member 44 a and the projectingportion 16. Therefore, the return disc 52 connects the first pistonmember 44 a and the projecting portion 16 so as to be incapable ofrotating relatively to each other, and the first piston member 44 a iskept at a withdrawal position by resilient force of a portion betweenthe mounting holes adjacent to each other.

The second piston member 44 b is accommodated in an annular secondgroove 30 b of the projecting portion 16 so as to be movable in theaxial direction. The second groove 30 b is formed so that, at the outerperipheral side of the first groove 30 a, the first groove 30 a and theouter side surface thereof are aligned with each other and the secondgroove 30 b opens into the bottom surface of the first groove 30 a. Thatis, the second groove 30 b is formed so that its inside diameter islarger than the inside diameter of the first groove 30 a and so that theinner surface of the second groove 30 b is positioned outwardly of theinner surface of the first groove 30 a in the radial direction.Therefore, the second piston member 44 b accommodated in the secondgroove 30 b is provided so that its sliding-disc-43-side end surfacefaces the first pressure-receiving surface 35 a at the first groove 30a. The second piston member 44 b is a member whose inside diameter islarger than that of the first piston member 44 a.

The second piston member 44 b has an projection provided at a portionthereof at the outer peripheral side of the sliding-disc-43-side endsurface in correspondence with the braking portion 44 c of the firstpiston member 44 a in the radial direction. Therefore, the second pistonmember 44 b can contact the first piston member 44 a at its projectingportion. The displacement of the second piston member 44 b causes thefirst piston member 44 a to receive a press-contact force from theprojecting portion of the second piston member 44 b.

An end surface at a side opposite to the sliding disc 43 of the secondpiston member 44 b corresponds to a second pressure-receiving surface 35b extending orthogonally to the clamp direction. In addition, a spacesurrounded by the second pressure-receiving surface 35 b and the secondgroove 30 b corresponds to the second pressure chamber 49 a to whichoperating fluid for displacing the second piston member 44 b issupplied.

As mentioned above, the second groove 30 b is formed so as to open intothe bottom surface of the annular first groove 30 a. That is, the areaof the bottom surface of the second groove 30 b is smaller than the areaof the bottom surface of the annular first groove 30 a. Therefore, thesecond pressure-receiving surface 35 b in the second piston member 44 baccommodated in the second groove 30 b is smaller than the firstpressure-receiving surface 35 a in the first piston member 44 aaccommodated in the first groove 30 a.

Further, the area of the first pressure-receiving surface 35 a is one inwhich the action of a predetermined pressure of an operating fluidcauses a press-contact force which causes the main shaft 4 a to be in acompletely clamped state to act upon the main shaft 4 a (the slidingdisc 43) by the braking portion 44 c. The area of the secondpressure-receiving surface 35 b is one in which a predetermined pressureof the operating fluid causes a press-contact force which causes themain shaft 4 a to be in a partially clamped state to act upon the mainshaft 4 a (the sliding disc 43) by the braking portion 44 c.

The operating fluid supplying mechanism 42 includes a first port 40 aand a second port 40 b (formed in the frame 2) a fluid supplying device41 connected to a first flow path 38 a and a second flow path 38 b(communicating with the first pressure-receiving surface 35 a and thesecond pressure-receiving surface 35 b, respectively) and to anoperating fluid supply source 101, and a first communicating path 39 aand a second communicating path 39 b (causing the first port 40 a andthe second port 40 b to communicate with the first flow path 38 a andthe second flow path 38 b, respectively).

More specifically, the first flow path 38 a is formed in the projectingportion 16, and communicates with the first pressure chamber 49 a at alocation facing the first pressure-receiving surface 35 a. In addition,the first flow path 38 a communicates with the first port 40 a (formedso as to open towards the outer surface of the casing member 28 a)through the first communicating path 39 a (formed in the casing member28 a). The first port 40 a is connected to the fluid supplying device 41provided separately from the frame 2.

The second flow path 38 b is formed in the projecting portion 16, andcommunicates with the second pressure chamber 49 b at a location facingthe second pressure-receiving surface 35 b. In addition, the second flowpath 38 b communicates with the second port 40 b (formed so as to opentowards the outer surface of the casing member 28 a) through the secondcommunicating path 39 b (formed in the casing member 28 a). The secondport 40 b is connected to the fluid supplying device 41 providedseparately from the frame 2.

The fluid supplying device 41 includes a selector valve (not shown),which is controlled by the controlling device of the machine tool. Oneside of the valve is connected to the operating fluid supply source 101and a tank 100 through fluid paths, and the other side of the valve isconnected to the first port 40 a and the second port 40 b through fluidpaths. The fluid supplying device 41 supplies operating fluid having apredetermined pressure from the common operating fluid supply source 101to the first port 40 a or the second port 40 b by selectively switchingbetween the first port 40 a and the second port 40 b by the selectorvalve. Accordingly, the fluid supplying device 41 selectively suppliesthe operating fluid having the predetermined pressure to at least one ofthe first and second pressure chambers. Therefore, the fluid supplyingdevice 41 corresponds to a switching portion 48 according to the presentinvention.

The fluid supplying device 41 is not limited to one that suppliesoperating fluids to the first port 40 a and the second port 40 b underthe same pressure. The fluid supplying device 41 may adjust the pressuresupplied to one of the first port 40 a and the second port 40 b foradjusting either one of the press-contact force that causes the mainshaft 4 a to be in the completely clamped state and the press-contactforce that causes the main shaft 4 a to be in the partially clampedstate.

Next, the operation of the rotation indexing device 1 shown in FIGS. 1and 2 will be described. First, in the rotation indexing device 1, whenthe circular table 5 is rotationally driven, the DD motor 9 is excitedby control of the controlling device of the machine tool. By generationof a rotating magnetic field due to the excitation, the motor rotor 7causes the main shaft 4 a, the flange 4 b, and the circular table 5 torotate. The rotational angle (amount of rotation) of the circular table5 at this time is detected by the rotation detector 20.

When a workpiece on the circular table 5 is processed while rotating themain shaft 4 a by a preset rotational angle and indexing the angularposition of the main shaft 4 a, the rotation indexing table 1 is suchthat the main shaft 4 a is kept at the indexed angular position by theclamping device 10 so as to be unrotatable. More specifically, afterindexing the angular position of the main shaft 4 a by driving the DDmotor 9, the controlling device of the machine tool causes operatingfluid to be supplied to only the first port 40 a by the selector valve(not shown) of the fluid supplying device 41 (switching portion 48) ofthe operating fluid supplying mechanism 42.

This causes the pressure of the operating fluid to act upon the firstpressure chamber 49 a. The entire first pressure-receiving surface 35 areceives the pressure of the operating fluid, so that the first pistonmember 44 a is displaced towards the sliding disc 43. This causes theclamp surface 63, provided at the end of the braking portion 44 c at thefirst piston member 44 a, to press-contact one of sliding surfaces 55 ofthe sliding disc 43, so that the sliding disc 43 is flexed and deformed.The other sliding surface 55 of the sliding disc 43 comes into contactwith the clamp surface 63 at the base portion 11. As a result, thebraking portion 44 c causes a press-contact force to act upon thesliding disc 43 serving as a portion of the main shaft 4 a.

The press-contact force that the braking portion 44 c of the firstpiston member 44 a causes to act upon the sliding disc 43 at this timecorresponds to the pressure that the entire first pressure-receivingsurface 35 a receives from the operating fluid. As mentioned above, thearea of the first pressure-receiving surface 35 a is one in which apredetermined pressure causes the press-contact force which causes themain shaft 4 a to be in a completely clamped state to act upon thesliding disc 43. Therefore, frictional resistance generated between theclamp surfaces 63 and the sliding surfaces 55 at this time does notallow rotational resistance applied to the main shaft 4 a by theclamping device 10 to rotate the main shaft 4 a, so that the clampingdevice 10 causes the main shaft 4 a to be in the completely clampedstate. That is, the clamping device 10 functions as a device thatmaintains the angular position of the main shaft 4 a of the rotationindexing table device 1.

When the fluid supplying device 41 (switching portion 48) causes theflow path to communicate with the tank 100, the pressure of theoperating fluid no longer acts upon the first pressure chamber 49 a,thereby reducing the internal pressure of the first pressure chamber 49a. By this, the pressure of the operating fluid also no longer acts uponthe first pressure-receiving surface 35 a, as a result of which thebraking portion 44 c of the first piston member 44 a no longer causesthe press-contact force to act upon the sliding disc 43. Therefore, thefirst piston member 44 a is returned to the withdrawal position byresilient force of the sliding disc 43 and resilient force of the returndisc 52. By this, the clamp surfaces 63 and the sliding surfaces 55 areseparated from each other, so that the clamping device 10 of therotation indexing table device 1 is in an unclamp state.

When a finishing operation is performed on a workpiece while rotatingthe circular table 5 in the rotation indexing table device 1, the fluidsupplying device 41 (switching portion 48) is controlled by thecontrolling device of the machine tool as in the previous example, sothat operating fluid is supplied to the second port 40 b.

This causes the pressure of the operating fluid to act upon the secondpressure chamber 49 b, the second pressure-receiving surface 35 b toreceive the pressure of the operating fluid, the second piston member 44b to be displaced towards the sliding disc 43, and an end of the secondpiston member 44 b to press the end surface at the side opposite to thesliding disc 43 at the first piston member 44 a, that is, the firstpressure-receiving surface 35 a. This also causes the first pistonmember 44 a to be displaced towards the sliding disc 43, the clampsurface 63 (braking surface) at the end of the braking portion 44 c atthe first piston member 44 a to contact one of the sliding surfaces 55of the sliding disc 43, and the second piston member 44 b topress-contact the sliding disc 43 through the first piston. Then, thesliding disc 43 receives a press-contact force by the second pistonmember 44 b through the first piston member 44 a, and, thus, is flexedand deformed. In addition, the other sliding surface 55 contacts theclamp surface 63 (braking surface) at the base portion 11.

Regarding the press-contact force of the second piston member 44 b atthis time, as mentioned above, the area of the second pressure-receivingsurface 35 b of the second piston member 44 b is smaller than the areaof the first pressure-receiving surface 35 a of the first piston member44 a. Therefore, even if pressure that is the same as that acting uponthe first pressure chamber 49 a acts upon the second pressure chamber 49b when the main shaft 4 a is set in the completely clamped state, thepress-contact force that the second piston member 44 b causes to actupon the sliding disc 43 is smaller than the press-contact force thatthe first piston member 44 a causes to act upon the sliding disc 43 whenthe main shaft 4 a is set in the completely clamped state. Consequently,operating fluid having a predetermined pressure is supplied from thecommon operating fluid supply source 101 to the common fluid supplyingdevice 41 (switching portion 48). The press-contact force that the firstpiston member 44 a causes to act upon the sliding disc 43 is smallerwhen the predetermined pressure acts upon the second pressure chamber 49b than when the predetermined pressure acts upon the first pressurechamber 49 a. This also causes a flexing amount of the sliding disc 43to be smaller.

Further, the area of the second pressure-receiving surface 35 b is onein which the predetermined pressure of the operating fluid causes thepress-contact force that causes the main shaft 4 a to be in thepartially clamped state to act upon the sliding disc 43 by the brakingportion 44 c. Therefore, frictional force generated between the slidingsurfaces 55 and the clamp surfaces 63 (braking surfaces) at this time isone allowing rotational resistance applied to the main shaft 4 a by theclamping device 10 to rotate the main shaft 4 a, so that the clampingdevice 10 causes the main shaft 4 a to be in the partially clampedstate. That is, in this case, the clamping device 10 functions as apartially clamping device, and the rotation indexing table device 1rotates while the main shaft 4 a is in the partially clamped state.

By the rotational resistance, variations in load from a cutter, whichprocesses a workpiece, in the rotation indexing table device 1 when afinishing operation is performed on the workpiece while rotating it arereduced. Therefore, it is possible to reduce deviations in therotational angle (the amount of rotation) of the rotation indexing tabledevice 1 resulting from the variations in load from the cutter. Thismakes it possible to also reduce pulsation in the controlling of the DDmotor 9 that is performed while correcting the deviation of therotational angle (the amount of rotation). Therefore, the rotation stateof the rotation indexing table device 1 can be stabilized to a uniformstate. Since the clamping device 10 in the partially clamp stateprovides rigidity to the main shaft 4 a in the rotation indexing tabledevice 1, it is possible to increase the rigidity of the main shaft 4 awithout increasing the size of the bearings 3. As a result, it ispossible to provide good surface roughness of a finished surface of theworkpiece when a finishing operation is performed on the workpiece whilerotating it by the clamping device 10 in the partially clamp state. Inaddition, it is possible to use a workpiece that is larger than arelated workpiece using bearings 3 of the same diameter. Accordingly,since bearings 3 having a smaller diameter can be used, a highprocessing precision can be realized, and manufacturing costs of therotation indexing table device 1 for the machine tool can be reduced.Further, without adjusting the pressure of the operating fluid that isthe same as that of the common operating fluid supply source 101, thepreset press-contact force that causes the main shaft 4 a to be in thepartially clamped state and the preset press-contact force that causesthe main shaft 4 a to be in the completely clamped state can be causedto act upon the main shaft 4 a by the braking portion 44 c of theclamping device 10.

In the embodiment shown in FIGS. 1 and 2, the first piston member 44 aand the second piston member 44 b are formed as two separate members.However, the present invention is not limited thereto. The first pistonmember 44 a and the second piston member 44 b may be formed as onemember (clamp piston).

Next, a rotation indexing table device 1 according to a anotherembodiment of the present invention will be described with reference toFIGS. 3 and 4. FIG. 3 is a general view thereof, and shows an exemplarystructure in which a clamp sleeve clamping device is used as a clampingdevice 110 of the rotation indexing table device 1. The rotationindexing table device 1 according to the embodiment has substantiallythe same structure as that shown in FIGS. 1 and 2 except that thestructure of the clamping device 110 differs and that a sliding disc 43that is mounted to the main shaft 4 a is not provided. Therefore, partscorresponding to those shown in FIGS. 1 and 2 are given the samereference numerals in FIGS. 3 and 4, and will not be described below.

In FIG. 3, the clamping device 110 is a clamp sleeve clamping device inwhich a press-contact force (rotational resistance) is caused to actupon a main shaft 4 a by a clamp sleeve 64 serving as a braking member.The clamping device 110 includes the clamp sleeve 64 (serving as abraking member), a first pressure chamber 36 a, a second pressurechamber 36 b, and an operating fluid supplying mechanism 42.

According to the embodiment shown in FIG. 3, the clamp sleeve 64includes a cylindrical clamp portion 64 a and a flange portion 64 b. Thecylindrical clamp portion 64 a is disposed between a base portion 11 ata frame 2 and a holding portion 23 at a circular table 5. The flangeportion 64 b extends radially consecutively with the clamp portion 64 a.The clamp portion 64 a is fitted and mounted to the outer side of thebase portion 11, and is mounted to a base member 29 at the frame 2through the flange portion 64 b with a mounting bolt 37. The clampportion 64 a is disposed so as to face and so as to be out of contactwith the inner peripheral surface of the holding portion 23 serving as asliding surface 33. The clamp portion 64 a is in close contact with theouter peripheral surface of the base portion 11 through three seals 34.

The clamp sleeve 64 has two grooves (a first groove 30 a and a secondgroove 30 b) formed in the inner peripheral surface of the clamp portion64 a, and portions thereof corresponding to the grooves are thin-walledportions that are thin. A space surrounded by the inner surface of oneof the grooves and the outer peripheral surface of the base portion 11and a space surrounded by the inner surface of the other groove and theouter peripheral surface of the base portion 11 are a first pressurechamber 36 a and a second pressure chamber 36 b to which operating fluid(such as pressure oil) is supplied. In the clamp sleeve 64, operatingfluid is supplied to the first pressure chamber 36 a and the secondpressure chamber 36 b, so that the thin-wall portions (provided incorrespondence with the first groove 30 a and the second groove 30 b)flex radially outward, thereby causing a press-contact force to act uponthe main shaft 4 a. Therefore, these thin-walled portions correspond tobraking portions. The radially outward direction corresponds to adirection in which the braking portions cause the press-contact force toact upon the main shaft 4 a. Surfaces at the sides of the first andsecond pressure chambers 36 a and 36 b in the thin-walled portions (thatis, a first braking portion 31 a and a second braking portion 31 b),provided in correspondence with the first groove 30 a and the secondgroove 30 b, correspond to a pressure-receiving surface 35 a and apressure-receiving surface 35 b, respectively.

In the embodiment, the first and second braking portions 31 a and 31 bare formed so that the areas of the pressure-receiving surfaces (thatis, the first and second pressure-receiving surfaces 35 a and 35 b)differ from each other, and so that their thicknesses (dimensions in theradial direction) differ from each other. The first and second brakingportions 31 a and 31 b are formed as a braking portion that generates apress-contact force for achieving a completely clamped state and abraking portion that generates a press-contact force for achieving apartially clamped state.

More specifically, the first braking portion 31 a is such that itsthickness and the area of the first pressure-receiving surface 35 a areset so as not to allow rotation of the main shaft 4 a caused by apress-contact force (rotational resistance) generated by a clamp surface32 and a sliding surface 33 due to a predetermined pressure that thefirst pressure-receiving surface 35 a receives by operating fluidsupplied from a common operating fluid supply source 101. That is, thethin-walled portions are formed thin so that they can flex easily. Thearea of the first pressure-receiving surface 35 a is such that, due tothe relationship with the thickness of the thin-walled portion, apress-contact force that causes the main shaft 4 a to be in thecompletely clamped state acts upon the main shaft 4 a by the action ofthe predetermined pressure of the operating fluid.

The second braking portion 31 b is formed as follows. That is, in ordernot to allow rotation of the main shaft 4 a caused by a press-contactforce (rotational resistance) generated by the clamp surface 32 and thesliding surface 33 due to a predetermined pressure that the secondpressure-receiving surface 35 b receives by operating fluid suppliedfrom the common operating fluid supply source 101, the thin-walledportion is thicker than that of the thin-walled portion corresponding tothe first braking portion 31 a, the pressure-receiving surface 35 b ismade narrower than the first pressure-receiving surface 35 a, andflexing amount and the press-contact force are less than those of thefirst braking portion 31 a.

Although the first and second braking portions 31 a and 31 b are formedso that the areas of the first and second pressure-receiving surfaces 35a and 35 b differ from each other and so that their thicknesses differfrom each other as in the illustrated embodiment, the present inventionis not limited thereto. Only the areas of the first and secondpressure-receiving surfaces 35 a and 35 b may differ from each other, oronly the thicknesses of the thin-walled portions may differ from eachother.

The first pressure chamber 36 a and the second pressure chamber 36 b areconnected to a fluid supplying device 41 (switching portion 48) of theoperating fluid supplying mechanism 42 through different paths, that is,a first flow path 38 a and a second flow path 38 b (formed in the basemember 29 of the frame 2), and a first communicating path 39 a and asecond communicating path 39 b and a first port 40 a and a second port40 b (formed in a casing member 28 a), respectively.

Next, the operation of the rotation indexing table device 1 shown inFIGS. 3 and 4 will be described. First, when a workpiece on the circulartable 5 is to be processed with the angular position of the main shaft 4a being indexed by rotating the main shaft 4 a by a preset rotationalangle, after indexing the angular position of the main shaft 4 a bydriving a DD motor 9, operating fluid is supplied only towards the firstport 40 a by a selector valve (not shown) in the liquid supplying device41 (switching portion 48).

This causes the pressure of the operating fluid from the operating fluidsupply source 101 to act upon the first pressure chamber 36 a. By this,the first pressure-receiving surface 35 a receives the pressure of theoperating fluid, and, as shown by dotted lines in FIG. 4, the firstbraking portion 31 a is deformed (flexed) in a diameter increasingdirection and the clamp surface 32 comes into contact with the slidingsurface 33. As a result, the first braking portion 31 a causes apress-contact force to act upon the main shaft 4 a.

As mentioned above, the first braking portion 31 a is such that itsthickness and the area of the first pressure-receiving surface 35 a areset so that a rotational resistance does not allow rotation of the mainshaft 4 a caused by a press-contact force acting upon the slidingsurface 33 by the clamp surface 32 when a predetermined pressure actsupon the first pressure-receiving surface 35 a. Therefore, at this time,frictional resistance generated between the clamp surface 32 and thesliding surface 33 does not allow the rotational resistance applied tothe main shaft 4 a by a clamping device 110 to rotate the main shaft 4a. Consequently, the clamping device 110 sets the main shaft 4 a in thecompletely clamped state. That is, in this case, the clamping device 10functions as a completely clamping device that maintains the angularposition of the main shaft 4 a.

On the other hand, when a finishing operation is to be performed on aworkpiece while rotating the circular table 5, a controlling device of amachine tool causes operating fluid to be supplied to the second port 40b by the selector valve in the liquid supplying device 41 (switchingportion 48) of the operating fluid supplying mechanism 42.

This causes the pressure of the operating fluid to act upon the secondpressure chamber 36 b. The second pressure-receiving surface 35 breceives the pressure of the operating fluid, and the second brakingportion 31 b is deformed (flexed) in a diameter increasing direction andthe clamp surface 32 press-contacts the sliding surface 33. As a result,the second braking portion 31 b causes a press-contact force to act uponthe main shaft 4 a.

The second braking portion 31 b is such that its thickness and the areaof the second pressure-receiving surface 35 b are set so that apress-contact force that acts upon the sliding surface 33 by the clampsurface 32 when a predetermined pressure acts upon the secondpressure-receiving surface 35 b causes the main shaft 4 a to be in thepartially clamped state. Therefore, frictional resistance generatedbetween the clamp surface 32 and the sliding surface 33 at this timeallows rotational resistance applied to the main shaft 4 a by theclamping device 110 to rotate the main shaft 4 a, so that the clampingdevice 110 causes the main shaft 4 a to be in the partially clampedstate. That is, in this case, the clamping device 110 functions as apartially clamping device, and the rotation indexing table device 1rotates while in the partially clamp state.

In the embodiment shown in FIGS. 3 and 4, the clamp sleeve 64 is anintegrated member having two grooves (that is, the first groove 30 a andthe second groove 30 b). However, as shown in FIG. 5, the clamp sleeve64 may be formed of two members, that is, a first member and a secondmember, and grooves may be formed in the members. In FIG. 5, the secondmember and the aforementioned bearing holder 14 are integrally formedwith each other, and a flange portion of the second member serves as thebearing holder.

A rotation indexing table device 1 according to still another embodimentof the present invention will be described with reference to FIGS. 6 and7. FIG. 6 is a general view thereof, and shows an exemplary structure inwhich a disc clamping device is used as a clamping device 210 of therotation indexing table device 1. The rotation indexing table device 1according to the embodiment has substantially the same structure as thatshown in FIGS. 1 and 2 except that the structure of the clamping device210 differs. Therefore, parts corresponding to those shown in FIGS. 1and 2 are given the same reference numerals in FIGS. 6 and 7, and willnot be described below.

In FIG. 6, the clamping device 210 causes a press-contact force(rotational resistance) to act upon a sliding disc 43, mounted to a mainshaft 4 a, by a clamp piston 44 (serving as a braking member), and is adisc clamping device as in the embodiment shown in FIGS. 1 and 2.Similarly to the previous embodiments, the clamp piston includes a firstpressure-receiving surface 35 a and a second pressure-receiving surface35 b. However, in the embodiment, as a portion that differs from that inthe embodiment shown in FIGS. 1 and 2, the second pressure-receivingsurface 35 b is provided with an unclamping function.

The clamp piston 44 serving as a braking member is formed as a singlemember in the illustrated embodiment. The clamp piston 44 isaccommodated in an annular first groove 30 a, formed in a projectingportion 16, so as to be movable in an axial direction. The first groove30 a is formed in a portion facing the sliding disc 43 in the projectingportion 16 so as to open towards the sliding disc 43. Therefore, theclamp piston 44 accommodated in the first groove 30 a is such that itscircular-table-5-side end surface (=sliding-disc-43-side end surface)faces the sliding disc 43.

The clamp piston 44 is provided with an annular projecting portion at aportion situated at the outer peripheral side of thesliding-disc-43-side end surface so as to face the clamp surface 63. Theprojecting portion contacts the sliding disc 43 and causes apress-contact force to act thereupon when the clamp piston 44 isdisplaced towards the sliding disc 43, and corresponds to a brakingportion 44 c according to the present invention. In the embodiment, thebraking portion 44 c causes a press-contact force to act upon thesliding disc 43 in the direction of the circular table 5 in the axialdirection. This direction corresponds to “a first direction, which isthe same as a direction in which the braking portion causes thepress-contact force to act upon the main shaft,” in the presentinvention.

The clamp piston 44 has an annular projecting portion 44 b formed in thelower end of the inner peripheral portion thereof and projecting towardsthe inner peripheral side. The inner peripheral surface of theprojecting portion 44 b is in close contact with the inner peripheralsurface of the first groove 30 a through a seal 34.

At a location between the projecting portion 44 b and the sliding disc43, an annular flange member 62 is mounted to a sliding-disc-43-side endsurface of the projecting portion 16 with a mounting bolt 60. The outerperipheral surface of the flange member 62 is in close contact with theinner peripheral surface of the clamp piston 44 through a seal 34.

A space surrounded by the lower end surface of the clamp piston 44 (endsurface at a side opposite to the sliding disc 43) including theprojecting portion 44 b and the first groove 30 a is a first pressurechamber 49 a. A space surrounded by the sliding-disc-43-side end surfaceof the projecting portion 16, the inner peripheral surface of the clamppiston 44, the flange member 62, and the inner peripheral surface of thefirst groove 30 a is a second pressure chamber 49 b is a second pressurechamber 49 b to which operating fluid is supplied for causing theclamping device 210 to be in an unclamp state while the clamp piston 44is displaced in a direction opposite to the first direction, that is, apress-contact force of the clamp piston 44 does not act upon the slidingdisc 43.

Here, the lower end surface of the clamp piston 44 corresponds to thefirst pressure-receiving surface 35 a extending in a second direction(which is orthogonal to the first direction) and receiving the pressureof an operating fluid in the first direction. Further, asliding-disc-43-side end surface of the projecting portion 44 b of theclamp piston 44, that is, a surface facing the flange member 62corresponds to the second pressure-receiving surface 35 b extending inthe second direction and receiving the pressure of operating fluid in adirection opposite to the first direction.

Spring members 61 are provided in the first pressure chamber 49 a. Thespring members 61 are compression springs and are provided between thebottom surface of the first groove 30 a and the first pressure-receivingsurface 35 a. Spring force acts upon the first pressure-receivingsurface 35 a to urge the clamp piston 44 in the first direction. Themagnitude of the spring force of each spring member 61 is set so that apress-contact force that causes the main shaft 4 a to be in a partiallyclamped state acts upon the main shaft 4 a by the braking portion 44 c.

The area of the first pressure-receiving surface 35 a is such that apress-contact force that causes the main shaft 4 a to be in a completelyclamped state by the action of a predetermined pressure of an operatingfluid as well as the action of the spring force of each spring member 61is caused to act upon the main shaft 4 a (sliding disc 43) by thebraking portion 44 c. The area of the second pressure-receiving surface35 b is such that a pressing force that is larger than the urging forceis caused to act upon the spring member 61 by the clamp piston 44 as aresult of the action of the predetermined pressure of the operatingfluid.

Accordingly, the first pressure chamber 49 a functions as a pressurechamber that generates a press-contact force for achieving a completelyclamped state, and the second pressure chamber 49 b functions as apressure chamber that generates a force opposing the urging force ofeach spring member 61 for achieving an unclamped state.

A first flow path 38 a of an operating fluid supplying mechanism 42 isformed in the projecting portion 16, and communicates with the firstpressure chamber 49 a at a location facing the first pressure-receivingsurface 35 a. The first flow path 38 a communicates with a first port 40a (formed so as to open towards the outer surface of a casing member 28a) through a first communication path 39 a (formed in the casing member28 a). The first port 40 a is connected to a fluid supplying device 41provided separately from a frame 2.

A second flow path 38 b is formed in the projecting portion 16, andcommunicates with the second pressure chamber 49 b at a location betweenthe second pressure-receiving surface 35 b and the flange member 62 atthe inner peripheral surface of the first groove 30 a. The second flowpath 38 a communicates with a second port 40 b (formed so as to opentowards the outer surface of the casing member 28 a) through a secondcommunication path 39 a (formed in the casing member 28 a). The secondport 40 b is connected to the fluid supplying device 41 providedseparately from the frame 2.

Next, the operation of the rotation indexing table device 1 shown inFIGS. 6 and 7 will be described. First, when the angular position of themain shaft 4 a is to be indexed, as in the previous embodiments, thefluid supplying device 41 (switching portion 48) is controlled by acontrolling device of a machine tool, and operating fluid is supplied tothe second port 40 b.

This causes the pressure of the operating fluid from the operating fluidsupply source 101 to act upon the second pressure chamber 49 b, thesecond pressure-receiving surface 35 b to receive the pressure of theoperating fluid, and the clamp piston 44 to be pushed in a directionopposite to the first direction. In addition, the clamp piston 44opposes the urging force of each spring member 61 and is displaced inthe direction opposite to the first direction, so that the clamp surface63 (braking surface) at an end of the braking portion 44 c of the clamppiston 44 is separated from one of sliding surfaces 55 of the slidingdisc 43. Therefore, the clamping device 210 indexes the angular positionof the main shaft 4 a by driving a DD motor 9.

After indexing the angular position as mentioned above, when processingis performed in a completely clamped state, the fluid supplying device41 (switching portion 48) causes a flow path at a side of the secondport 40 b to communicate with a tank 100 and causes operating fluid tobe supplied to a flow path at a side of the first port 40 a. By this,the pressure of the operating fluid no longer acts upon the secondpressure chamber 49 b, and acts upon the first pressure chamber 49 a.The first pressure-receiving surface 35 a receives the pressure of theoperating fluid in addition to the urging force of each spring member61, and the clamp piston 44 is displaced towards the sliding disc 43. Inaddition, as shown in FIG. 7, the clamp surface 63 at the end (brakingportion 44 c) of the clamp piston 44 press-contacts one of the slidingsurfaces 55 of the sliding disc 43, thereby flexing and deforming thesliding disc 43. The other sliding surface 55 of the sliding disc 43press-contacts the clamp surface 63 at the base portion 11.

Here, the frictional resistances generated between the clamp surfaces 63and the sliding surfaces 55 do not allow the rotational resistanceapplied to the main shaft 4 a by the clamping device 210 to rotate themain shaft 4 a.

On the other hand, when a finishing operation is performed on aworkpiece by rotating it, the fluid supplying device 41 (switchingportion 48) causes the flow paths for the first and second ports 40 aand 40 b to communicate with the tank 100.

As a result, the pressure of the operating fluid no longer acts upon thefirst pressure chamber 49 a and the second pressure chamber 49 b,thereby reducing the internal pressures of the first and second pressurechambers 49 a and 49 b. Since the pressure of the operating fluid nolonger acts upon the first pressure-receiving surface 35 a and thesecond pressure-receiving surface 35 b too, the first pressure-receivingsurface 35 a only receives the urging force of each spring member 61.Therefore, the braking portion 44 c of the clamp piston 44 causes apress-contact force to act upon the sliding disc 43 by only the urgingforce of each spring member 61. Frictional forces between the slidingsurfaces 55 and the clamp surfaces 63 (braking surfaces) at this timeallow the rotational resistance applied to the main shaft 4 a by theclamping device 210 to rotate the main shaft 4 a. The clamping device210 causes the main shaft 4 a to be in a partially clamped state. Thatis, the clamping device 210 functions as a partially clamping device,and the rotation indexing table device 1 rotates while the main shaft 4a is in the partially clamped state.

Although, in the embodiment shown in FIGS. 6 and 7, the braking portion44 c is formed so as to directly push the sliding disc 43, the presentinvention is not limited thereto. As shown in FIG. 8, the brakingportion 44 c may be formed so as to push the sliding disc 43 through areturn disc 45.

In the embodiment shown in FIGS. 6 and 7, in the partially clampedstate, the sliding disc 43 is such that one of the sliding surfaces 55receives a press-contact force from the braking portion 44 c and theother sliding surface 55 press-contacts the clamp surface 63 at the baseportion 11. However, the present invention is not limited thereto. Thesliding disc 43 may be such that the other sliding surface 55 does notcontact the clamp surface 63 at the base portion 11, and only the one ofthe sliding surfaces 55 contacts the braking portion 44 c while the oneof the sliding surfaces 55 receives a press-contact force.

Further, although, in the embodiment shown in FIGS. 6 and 7, the clamppiston 44 is formed as a single member, the present invention is notlimited thereto. As shown in FIG. 9, the clamp piston 44 may include twopiston members, that is, a piston member 44 a and a piston member 44 b.

The clamping device of the main shaft driving device in the machine toolaccording to the present invention is mounted to the machine tool as aninstallation device of the machine tool or as a device attached later tovarious machine tools.

1. A clamping device in a main shaft driving device for a machine tool,the main shaft driving device rotationally driving a main shaft by adriving device, the main shaft being rotatably supported by a frame andhaving a member that is rotationally driven secured to an end portionthereof, the clamping device comprising: a clamp piston provided so asto be displaceable in an axial direction of the main shaft with respectto the frame, the clamp piston including a pressure-receiving surfaceand a braking portion, the pressure-receiving surface receiving pressureof an operating fluid, the braking portion causing a press-contact forceto act upon the main shaft; a pressure chamber formed by thepressure-receiving surface and the frame; and an operating fluidsupplying mechanism provided for supplying the operating fluid from anoperating fluid supply source to the pressure chamber, wherein thepress-contact force is caused to act upon the main shaft by displacingthe clamp piston towards the main shaft by the pressure of the operatingfluid that is supplied to the pressure chamber, wherein the clampingdevice includes a spring member that urges the clamp piston in a firstdirection, which is the same as a direction in which the braking portioncauses the press-contact force to act upon the main shaft, the springmember causing a spring force to act upon the pressure-receivingsurface, the spring force causing the press-contact force that causesthe main shaft to be set in a partially clamped state to act upon themain shaft by the braking portion, wherein the clamp piston has a firstpressure-receiving surface and a second pressure-receiving surface, thefirst pressure-receiving surface extending in a second direction that isorthogonal to the first direction and receiving pressure of an operatingfluid in the first direction, the first pressure-receiving surfacereceiving the spring force of the spring member, the secondpressure-receiving surface extending in the second direction andreceiving pressure of an operating fluid in a direction opposite to thefirst direction, and wherein the operating fluid supplying mechanismincludes a switching portion that selectively supplies the correspondingoperating fluid from a common operating fluid supply source to at leastone of a first pressure camber and a second pressure chamber, the firstpressure chamber being formed by the first pressure-receiving surfaceand the frame, the second pressure chamber being formed by the secondpressure-receiving surface and the frame.